1. Field of the Invention
The present invention pertains to an improved method of analyzing fluids and an apparatus, such as an ion chromatograph, in which fluid samples are automatically injected into a detection unit in both diluted and undiluted conditions for simultaneous determination of the concentration of major and minor components of the fluid.
2. Background
Laboratory analysis of fluid samples in large numbers is carried out routinely. For example, in the petroleum exploration and production industry the analysis of various brines obtained from sea water, ground water and process samples are carried out with ion chromatographs and other spectrographic devices. The wide range of concentrations of the ionized components often requires dilution of the fluid samples to make possible the measurement of high concentrations of certain ions which, if the sample is not diluted, are present at concentrations beyond the measurement range of the detector. In some instances, if a fluid sample is not diluted before analysis, the major components cannot be quantified because they are present in concentrations beyond the linear response region of the detector device, the purity of recorded peaks or maximum concentrations having large elution volumes is questioned due to the tendency of adjacent peaks on the chromatogram to overlap as the concentration of one or both components increase, or retention times cannot be used for identification purposes because of abnormal readings and certain ion migration phenomena.
Conversely, if the fluid sample is diluted to lower the concentration of the so-called major ion components, one or more of the minor components to be measured cannot be reliably determined because their concentrations become close to or less than the limit of detection. As a result, a two step analysis is required which can be very time consuming and expensive when large numbers of samples are required to be measured. Accordingly, the present invention is directed to improvements in ion chromatograph methods and systems for measuring the ion concentrations in fluid samples, which improvements eliminate the need to prepare and inject into the chromatograph detection unit different standard solutions or prepare and handle a particular fluid sample twice, namely, in both diluted and undiluted concentrations.
The desired results of the present invention include obtaining the concentrations of all of the components of a fluid sample in a single graphic or numerical display such that a single chromatogram will show the concentrations of all components. Accordingly, significant savings in time for analyzing a particular type of fluid is realized by the improved method and apparatus of the invention.